Aquaculture Reports (Apr 2024)
Condition factor tailored to lumpfish (Cyclopterus lumpus) used as cleaner fish in salmonid farms
Abstract
Lumpfish (Cyclopterus lumpus) are extensively used as part of the control measures against salmon lice in fish farms. In recent years, there has been an increased focus on lumpfish welfare, and how to increase survival of lumpfish during production. To survey lumpfish welfare and compare welfare between different fish farms, welfare indicators are necessary. Condition factor is an attractive welfare indicator since it depends only on the length and weight of the fish, which is easy to measure and does not require euthanisation. Fulton’s K is commonly used to assess body condition for fish. However, this condition factor assumes isometric growth, which has been found not to be a reasonable assumption for lumpfish. In this study, we suggest an alternative expression for lumpfish body condition, which is based on almost 30 000 lumpfish sampled from Norwegian fish farms during production. The resulting condition factor is given as 5.85 ⋅ W∕L2.5016, where W is the lumpfish weight measured in grams, and L is the standard length measured in centimetres. We demonstrate that our proposed condition factor is more suitable for comparing body condition of lumpfish than Fulton’s K, since Fulton’s K is negatively correlated to length such that small fish tend to have high Fulton’s K factors. We conclude that Fulton’s K is an inappropriate indicator of lumpfish welfare, and propose to rather use a condition factor tailored to lumpfish, like the presently proposed condition factor. We also illustrate why standard length (length up to the caudal fin) is more appropriate for measuring body condition than total length (i.e. length including the caudal fin). For condition based on standard length, we found that caudal fin erosion was less prevalent among the lumpfish with comparatively higher body condition. The same relationship was not found for body condition based on total length.
